The present invention relates to a new and improved construction of a hydraulic driven press for embossing, bending, stamping, especially for fine or precision blanking, which is of the type comprising a plunger or ram guided in a stand or support, this plunger or ram being supported by means of pressure chambers and a piston at the stand, such pressure chambers comprising at least one actuation pressure chamber and one counter pressure chamber.
During fine or precision blanking it is extremely important that the plunger or ram moves uniformly during the cutting operation, since otherwise there are not obtained clean cutting surfaces and the longevity of the tools is reduced.
With the heretofore known fine or precision blanking presses the desired cutting speed is achieved in that there is forced a certain quantity of oil into the punch cylinder by means of a pump or a volume regulator.
Experience has shown that the speed of the ram cannot be maintained constant because the forces which act upon the ram during the cutting operation continuously change due to a reduction of the cutting forces and material hardening, and owing to the hydraulic resilient action which prevails because of the build-up and relaxation of the oil column in the cylinder there arise deceleration and acceleration phenomenas at the ram. It is therefore necessary to select the cutting speed so small that the speed changes only have a slight effect upon the quality of the parts and the longevity or service life of the tools.